This invention relates in general to controlling mold temperature in a casting system to produce a cast article. Pressure pouring of molten metal from a furnace to fill a mold cavity has been used for several decades. At room temperature, the metal is solid and becomes fluidic when melted with sufficient heat.
It is known to use a low pressure countergravity casting apparatus to cast molten metal into a mold. One example of such an apparatus is described in U.S. Pat. No. 5,215,141. Basically, in a low pressure countergravity casting apparatus, molten metal is supplied to a machine furnace. The machine furnace includes a supply conduit for introducing a gas under pressure into the machine furnace. As the gas is introduced into the machine furnace, the molten metal in the machine furnace is forced through a submerged feed tube, or evacuation conduit, into the mold. The evacuation conduit is commonly referred to as a stalk tube. The mold receives the molten metal through holes in the bottom of the mold.
The molten metal must cool in the mold and harden to produce the cast article. Cooling of the molten metal is generally done by cooling the mold using a cooling fluid flowing through cooling channels in the mold. Conventionally, cooling of the mold has been controlled by a skilled human operator who adjusts the flow of the cooling fluid, which has been rather imprecise. Insufficient cooling times can lead to an improperly formed cast article. Excessive cooling time leads to decreased cycle times and economic inefficiency.
In order to make a solid cast article with the best possible structural properties in the least amount of time, the mold temperature during metal filling and during cooling must be accurately controlled regardless of environmental conditions (e.g., ambient air temperature, humidity, and temperature and pressure of the cooling fluid). During casting, the heat energy of the molten metal (e.g., aluminum) flows into the mold and then into the cooling fluid. Preferably, a temperature profile is achieved such that a directional solidification of the cast article occurs wherein the article solidifies from the outside and then in towards the filling area (i.e., stalk tube). After a solidified article is removed from the mold, it is prepared as quickly as possible for casting another part. This includes ensuring that the mold starts the next cycle at a predetermined temperature. Thus, it is desired to cool a mold as quickly as possible while maintaining acceptable structural properties of the article and providing directional solidification.
The above advantages as well as other advantages not specifically enumerated are achieved by a mold temperature control system comprising a mold section having a cavity, a fluid circuit to distribute a flow of a conditioning fluid, the fluid circuit being positioned spaced apart from the cavity, a temperature sensor positioned in the mold to generate a signal representative of a temperature in the mold, a controllable supply of the conditioning fluid, and a controller for automatically initiating flow of the conditioning fluid through the fluid circuit in response to an initiation temperature and for automatically terminating flow of the conditioning fluid through the fluid circuit in response to a termination temperature.
Various advantages of this invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiment, when read in light of the accompanying drawings.